Virtual reality (VR) with head-mounted displays (HMDs) is associated with a variety of applications. The ability to show wide field of view content to a user can be used to provide immersive visual experiences. A real-world environment has to be captured in all directions resulting in an omnidirectional image/video content corresponding to a sphere. With advances in camera rigs and HMDs, the delivery of VR content may soon become the bottleneck due to the high bitrate required for representing such a 360-degree image/video content. When the resolution of the omnidirectional video is 4K or higher, data compression/encoding is critical to bitrate reduction.
In general, the omnidirectional image/video content corresponding to the sphere is transformed into a sequence of images, each of which is a projection-based frame with a 360-degree image/video content represented by one or more projection faces arranged in a 360-degree Virtual Reality (360 VR) projection layout, and then the sequence of the projection-based frames is encoded into a bitstream for transmission.
However, it is possible that the employed 360 VR projection layout is not compact, and/or has many image content discontinuity edges that are caused by packing of projection faces. Encoding a projection-based frame with such a 360 VR projection layout may have poor coding efficiency, and/or may have poor image quality after compression.